The mechanical, electronic, thermal and tribiology properties of single-wall carbon nanotubes (SWCNTs), carbon nano-onions (CNO) and nanodiamond (ND) particles offer significant potential as components for the design of new materials (A. Hirsch, “Functionalization of single-walled carbon nanotubes,” Angew. Chem. Int. Ed Engl. 2002:41(11), pp. 1853-1859; S. Banerjee, T. Hemraj-Benny and S. S. Wong, “Covalent surface chemistry of single-walled carbon nanotubes,” Adv. Mater. 2005:17(1), pp. 17-29; Y. Show, M. A. Witek, P. Sonthalia, G. M. Swain, “Characterization and electrochemical responsiveness of boron-doped nanocrystalline diamond thin-film electrodes,” Chem. Mater. 2003:15, pp. 879-888; E. Wilks, J. Wilks, Properties and Applications of Diamond, 1997, Butterworth: Oxford, England; M. Choi, I. S. Altman, Y. J. Kim, P. V. Pikhitsa, S. Lee, G. S. Park, T. Jeong, J. B. Yoo, “Formation of shell-shaped carbon nanoparticles above a critical laser power in irradiated acetylene,” Adv. Mater. 2004:16, pp. 1721-1725; J. C Francis, Solid Lubricants and Self-Lubricating Solids, 1972, Academic Press: New York; Y. Liu, R. L. Vander Wal, V. N. Khabashesku, “Functionalization of carbon nano-onions by direct fluorination,” Chem. Mater. 2007:19(4), pp. 778-786, 2007). In spite of the promise offered by new materials based on these carbon nanostructures, processing difficulties resulting from the limited solubility of these species in common solvents has slowed the development of carbon nanostructure materials. Functionalization or derivatization of carbon nanostructures has been pursued as a means to increase their solubility in solvents and facilitate their incorporation into new materials and devices. Beneficial aspects resulting from properties of the functionalizing group may also be conferred to functionalized carbon nanostructures. Functionalized carbon nanostructures soluble in water are of particular interest due to this solvent's role in biological systems and its benign environmental impact. Water-soluble carbon nanostructures have attracted significant attention for biomedical applications, including biosensing and drug delivery (A. Bianco, K. Kostarelos, C. D. Partidos, M. Prato, “Biomedical applications of functionalized carbon nanotubes,” Chem. Commun. 2005, pp. 571-577).
Water solubilization of carbon nanostructures has been achieved through surface activation via strong oxidizing acid treatment and multi-step derivatization using coupling reactions, many of which utilize expensive PEG-based coupling reagents (A. Bianco, K. Kostarelos, C. D. Partidos, M. Prato, “Biomedical applications of functionalized carbon nanotubes,” Chem. Commun. 2005, pp. 571-577; A. S. Rettenbacher, B. Elliott, J. S. Hudson, A. Amirkhanian, L. Echegoyen, “Preparation and functionalization of multilayer fullerenes (carbon nano-onions),” Chem. Eur. J. 2005:12, pp. 376-387; A. Krüger, Y. Liang, G. Jane, J. Stegk, “Surface functionalization of detonation diamond suitable for biological applications,” J. Mater. Chem. 2006:16, pp. 2322-2328; J. J. Stephenson, J. L. Hudson, A. D. Leonard, B. K. Price, J. M. Tour, “Repetitive functionalization of water-soluble single-walled carbon nanotubes. addition of acid-sensitive addends,” Chem. Mater. 2007:19, pp. 3491-3498; F. Liang, J. M. Beach, P. K. Rai, W. Guo, R. H. Hauge, M. Pasquali, R. E. Smalley, W. E. Billups, “Highly exfoliated water-soluble single-walled carbon nanotubes,” Chem. Mater. 2006:18(6), pp. 1520-1524). The harsh conditions of oleum treatment may cause sidewall etching and impact the mechanical properties of the nanotube. Further, these conditions may be unsuitable for the sensitive functionalities sometimes required for biomedical applications.
Fluorinated SWCNTs may be reacted under mild conditions with various agents, including amino acids, urea, amino alcohols, and diols to produce stable suspensions in water (Y. Liu, Z. Gu, J. L. Margrave, V. N. Khabashesku, “Functionalization of nanoscale diamond powder: fluoro-, alkyl-, amino-, and amino acid-nanodiamond derivatives,” Chem. Mater. 2004:16, pp. 3924-3930; L. Zhang, V. U. Kiny, H. Peng, J. Zhu, R. F. M. Lobo, J. L. Margrave, V. N. Khabashesku, “Sidewall functionalization of single-walled carbon nanotubes with hydroxyl group-terminated moieties,” Chem. Mater. 2004:16, pp. 2055-2061). Although these materials may be dispersed as a suspension, they lack true solubility as a well dispersed solution having long term stability.
In light of the foregoing, it would be beneficial to provide additional water soluble carbon nanostructures and to develop methods for preparation thereof.